Arc gap



Jan. 1 11924 C. E. BENNETT ARC GAP Filed May 25, 1920 Patented Jan. 1, 192 4.

UNITED STATES 1,479,692 PATENT OFFICE.

CHARLES E. BENNETT, OF ATLANTA, GEORGIA, ASSIGHOB, BY KIBNE ASSIGN'KENTS, TO BALT MANUFACTURING COMPANY, OF ATLANTA, GEORGIA, A CORPORATION OF GEORGIA.

ARC GAP.

' Application filed Bay as, 1920. Serial llo. 504,221.

To all whom it may cmwem:

Be it known that I, CHARLES E. Bnnmrrr, a citizen of the United States of America, residing at Atlanta, in the county of Fulton and State of Georgia, have invented certain new and useful Improvements in Are Gaps, of which the following is a specification.

My invention relates to are gaps, and my object is to provide a a spark-over rating w ich is maintained substantially constant regardless of varying moisture conditions at the ga While this may be accomplished in di erent ways, I have indicated, as an embodiment of my ideas, a terminal construction of such character that the drop in the gap rating normally incident to the presence of moisture at the gap (as in a rain storm) is automatically compensated by the altered electrical conditions at the terminals.

In'the accompanyin drawings- Fig. 1 is a-broken si e elevation of an arc gap illustrative of my inventi6 1 '1 'gs. 2 and 3 are more or less diagrammatic views illustrating the lines of force between the gap terminals under dry and wet conditions,respectively;

Figs. 4 and 5 are more or less diagrammatic side elevations of modified constructions of the terminals; and

Fi 6 is an explanatory diagram.

While the present invention 1s susceptible of adaptation to various installations in which an arc gap ma be used, I have shown it in a form a plicab e to surge or lightning arresters of t e type illustrated in my conding application Serial No. 306,383, filed fme 24, 1919 designed to protect the equipment of an a ternatin current power line.

In an installation of t is type, the ground connection through the arrester requires an arc gap, the terminals of which are spaced a predetermined distance apart, depending upon the normal voltage of the protected line. The spacing of the terminals must be such that while no arc-over will occur under ordinary line conditions, such as harmless surges, yet when dangerous current is imposed u on the line, it will at once jump the gap an I discharge to ground without inquay to the equi ment installed in the line. he spacing or a given arc-over voltage differs with the character of the arc terminals; thus, for needle point terminals the p installation havingspacin must-be considerably greater than for sp ere terminals; while for sphere terminals, those of greater size may be set closer together than those of smaller size, for a given gap rating. The relative settlng for terminals of these ty s is illustrated in Fig. 6. As will be 0 served, the dlstancea between the needle terminals 7 1s considerably greater than the distance b between the sphere terminals 8; while the distance 0 between the large spheres 9 is still shorter.

One of the greatest external factors which afiect the gap rating is moisture in the form of fog, mist or rain. The efiect of rain on a sphere gap lowers the rating from to Its effect on a needle gap is much less, by reason of the reater normal spacing between the points and the fact that the latter gather little moisture upon their surfaces. But while a needle gap possesses this desirable characteristic, on the other hand it is objectionable for the reason that there is certain la (incident to corona formation) in the strilring of the arc across the gap. In an installation which requires as close an approximation to instantaneous action as can be attained. .such a delay is objectionable.

On the other hand, an are forms instantly between sphere terminals, and the use of the latter is therefore referred. 'But a sphere gap has .the drawack above noted, that ram eatly decreases the p rating, and excessive spacing between t e spheres is necessary to prevent grounding the line through 'the gap at normal voltage under wet weather conditions. This s acin renders the gap less sensitive than esire to take care of line surges which may occur under 'dry weather conditions. In other words, the gap between the fixed spheres 96 must be ad usted for wet weather conditions, and is thus not sufiiciently sensitive under dry weather conditions.

I have now discovered that this difliculty may be overcome by associating with the gap terminals a body of some material which is inactive under dr weather conditions, but becomes effective under wet weather conditions to counteract the decreased ratin of the gap. The ap terminals may t erefore be sensitive set to take care of sur under dry weat er conditions, and .sti be free from danger ofarc-over at line voltage under wet weather conditions.

Just what form, shape or substance is used for the associated terminal element is not essential so long as the desired effect is secured. In Fig. 1, however, I have shown the metallic spheres 8 substantially embedded in a body of insulating material 1Q, but exposed on their adjacent faces. The exposed metallic terminals are respectively connected by conductors 11 to metallic caps 12 and 13 mounted on the post insulators 14. The cap 12 is connected by lead 15 to the protected power line 16, while cap 13 is connected by lead 17 to ground through an arrester (not shown). The spacing between the metal terminals 8 is adjusted to that required to discharge a dangerous line surge by arc-over under dry weather conditions. The lines of force or electrostatic flux between the metallic spheres are diagrammatically illustrated at 18 in Fig. 2. Should a rain storm occur, however, which would normally so lower the gap rating that an arc-over at line voltage would normally follow, the water falling upon the insulating spheres 1O coats the latter with a conducting film and transforms their surfaces into conductors. The electrical conditions at the tenninals are thereby automatically so altered, that an arc-over does not take place. Observations have indicated a dispersion of the lines of force or electrostatic flux somewhat as indicated diagrammatically at 19, Fig. 3.

The particular nature of the material 10 is subject to considerable variation. I have found that while porcelain of the general type used in insulators, may under proper conditions serve the purpose satisfactorily, still better results are obtained when a more or less porous insulating material, such as lava, cement, or special clay compounds, is used, which not only affords a conducting surface-film of moisture, but is also permeated by the moisture so as to actually afford a conductor body when wet. The approximation to a metal terminal of large size is thus more close.

As above stated, the particular form of terminal, and of the associated normally insulating body, is subject to considerable variation. Thus, in Fig. 4 I have shown the sphere terminal in the form of a plate 20, and the associated insulating material in the form of a larger disc 21.

In Fig. 5 I have shown an insulator disc 21 of this type associated with a horn ap terminal 22 instead of the plate 20 of ig. 4. Various other constructions will readily occur to those dealing with the problem.

The underlying thought of the specific application of my invention is to provide a metallic gap terminal having associated therewith a nonconductor serving, when wet, to increase the electro-conductive area of the gap terminal. The electrostatic flux field between the gap terminals thus automatically expands and contracts, depending upon moisture conditions at the terminals, and thus automatically maintains the gap rating substantially constant, although the resistance of the ga varies. The particular nature of the associated element of the gap terminal is subject to variation, but I prefer a substance which, while an insulator when dry, is more or less readily permeated by moisture when wet.

Various adaptations and modifications of the invention will readily occur to those dealing with the problem, without departing from what I claim as my invention.

I claim 1. In the arc gap installation, a pair of electrodes operative when dry, and associated means 0 rative only when wet to compensate the owered impedance of the gap in the presence of moisture and serving to maintain the gap rating substantially uniform under wet and dry conditions.

2. In an arc gap installation, a pair of electrodes operative when dry, and associated means operative when wet to vary the electrostatic flux field at the gap, and to maintain the gap rating substantially constant.

3. In an arc-ga installation, a pair of spaced electrodes aving, when dry, a relatively restricted zone of electrostatic flux therebetween, and associated means serving, when wet, to enlarge said zone under moisture conditions at the gap.

4. In an arc-gap installation, metallic terminals and associated insulating bodies serving when wet to enlarge the conducting area of the terminals.

5. In an arc-gap installation, a metallic terminal and an associated insulator" electrically connected thereto under moisture conditions and serving to enlarge the conductin area of said terminal and thus to expan the electrostatic flux field at the gap.

6. In an arc-gap installation, a metallic terminal and an associated moisture permeable insulator electrically connected thereto and serving under moisture conditions to effectively enlarge the conductive area of said terminal.

7. In an arc-gap installation, a pair of electrodes, and means associated therewith. and responsive to moisture conditions at the gip for varying the electrostatic flux field tween the electrodes.

8. In an arc-gap installation, a pair of electrodes shrouded in moisture receiving insulator means associated with said terminals to vary the flux field between the same under wet and dry conditions at the gap.

9. In an arc-gap installation, a pair of spaced electrodes, and insulator means associated therewith and operative under moisture conditions at the gap to substantially prevent corona formation between the electrodes.

10. In an arc-gap installation, a metallic electrode and an associated moisture permeable insulator having a curvilinear surface facing the gap.

11. In an arc gap installation, a metallic electrode and an associated electrode surface electrically connectedthereto when wet and of a character serving to prevent globule formation thereon under moisture condi: tions at the gap. 2 V

12. In an arc gap installation, a metallic electrode and an-associated electrode surface of non-conducting material electrically connected in multiple to said metallic electrode b moisture.

13. The method of stabilizin an arc gap rating under wet and dry con itions at the gap, which comprises automatically varying the flux field between the gap terminals by moisture applied to the terminals.

14. The met 0d of stabilizin an arc gap rating under wet and dry con itions at the gap, which comprises automatically enlarging the conductin area of the terminals by the application 0 moisture thereto.

In testimony whereof I have signed my name to this specification.

CHARLES E. BENNETT. 

